1. Field of the Invention
The present invention relates to a process for producing methyl formate by the dehydrogenation of methanol.
Methyl formate is a product for chemical industries which is important as an intermediate to be used for producing organic chemicals such as dimethylformamide and formic acid, carbon monoxide and the like.
2. Description of Related Arts
It is known that methyl formate is produced by a process wherein methanol is carbonylized into methyl formate under pressure by the use of a catalyst such as sodium alcoholate according to the chemical equation CH.sub.3 OH+CO HCOOCH.sub.3 (1) or a process in which methanol is catalytically dehydrogenated into methyl formate according to the chemical equation 2CH.sub.3 OH HCOOCH.sub.3 +2H.sub.2 (2).
The production of methyl formate by the dehydrogenation of methanol is industrially put into practice at the present time due to the recent progress of development of catalysts and a variety of catalysts proposed. There are disclosed, as examples of dehydrogenation catalyst, a catalyst comprising copper and an element belonging to group 3a of the periodic table in Japanese Patent Publication No. 6412/1981; a catalyst comprising copper, an actinide and an rare-earth element in Japanese Patent Publication No. 46819/1978; a catalyst comprising copper, zinc, an oxide of aluminum and zirconium in Japanese Patent Publication No. 46821/1978; a catalyst comprising copper and a cement in Japanese Patent Publication No. 15820/1982; a catalyst comprising copper, calcium and a zirconium compound in Japanese Patent Publication No. 44655/1982; and a catalyst comprising copper, zinc, an oxide of aluminum, an alkali-metal compound and a phosphorus compound in Japanese Patent Publication No. 33418/1984 and Japanese Patent Application Laid-Open No. 151047/1991.
The production of methyl formate by the dehydrogenation of methanol usually attains only several tens percent of yield because of equilibrium conditions. In the case of carrying out the dehydrogenation reaction under pressure taking into consideration the collection of low boiling methyl formate, the yield thereof is further lowered. In the case of effecting the reaction in gaseous phase, therefore, it is forced to cool reactor outlet gas for separating gas from liquid, separate methyl formate from the mixture of the condensed methyl formate and unreacted methanol, and thereafter recycle a large amount of the separated methanol through the dehydrogenation reaction step, causing a disadvantage that a large amount of energy is required. If the problems of such low conversion efficiency in one pass system and the forced recycle of a large amount of methanol are solved, it is made possible to more efficiently produce methyl formate by the dehydrogenation of methanol.
In the production of methyl formate by the dehydrogenation of methanol in gaseous phase, the above-mentioned equilibrium restriction makes it impossible to achieve a high yield of methyl formate in one pass system.
Accordingly, in order to advantageously proceed with the reaction, the equilibrium restriction must be overcome. For the aforesaid purpose, for example, methyl formate or hydrogen as a reaction product may be withdrawn outside the reaction system to enable the reaction to proceed towards the formation of methyl formate. The aforementioned idea is disclosed, for example, in Japanese Patent Application Laid-Open No. 235846/1990. According to the disclosure therein, by the use of a reactor equipped with a hydrogen separating membrane, the hydrogen produced by the dehydrogenation of methanol is continuously withdrawn through the separating membrane outside the reaction system so as to proceed with the reaction. However, according to the working examples therein, the above-mentioned method shows improvements in methanol conversion efficiency and yield of methyl formate of only 2 to 13%, when compared at the same reaction temperature.
Under such circumstances, intensive research and investigation were accumulated by the present inventors, and finally the present invention has been accomplished.